Human chorionic gonadotropin is normally present in serum of males and non-pregnant females at concentrations below 10 mIU/ml. Structurally, hCG is a glycopeptide hormone (M.W.-40,000) consisting of two distinct amino acid chain subunits, designated as alpha and beta. Following conception, the concentration produced by the placenta during pregnancy in serum and urine alike increases steadily to a peak of as much as 100,000-200,000 mIU/ml at the 7th to 12th week. This increased level in the maternal system prevents normal involution of the corpus luteum and in the male fetus stimulates steroid production by the testes. Elevations of hCG are also found in trophoblastic neoplasms such as hydatidiform mole and choriocarcinoma.
Recently, the highly sensitive techniques of radioimmunoassay and enzymeimmunoassay have been applied to the analysis of hCG. Earlier radiometric assays utilized the intact biologically active hCG molecule as the antigen source for development of a binding entity. Since the pituitary hormones, thyroid stimulating hormone (TSH), follicle stimulating hormone (FSH) and luteinizing hormone (LH) also contain alpha subunits closely related to that of the hCG, the antibodies or membrane receptors for intact hCG produce non-specific binding and cross reaction with these hormones.
Chemically, CEA is a glycoprotein with a molecular weight of approximately 200,000 daltons that is secreted into the glycocalyx of gastrointestinal cells of the 2-6 month old human fetus. It was first presented as a specific antigen for adenocarcinoma of the colon. More recent studies however, have demonstrated CEA in a variety of malignancies and particularly those involving ectodermal tissue of gastrointestinal or pulmonary origin.
This multiplicity of antigen expression as well as the existence of potentially cross reacting compounds has limited the diagnostic value of many potential tumor markers. The prognostic utility of CEA when employed as a monitoring device has however been well established for several types of carcinoma. In general, a persistently elevated CEA finding following treatment is indicative of continuing disease whereas a decreasing value represents a favorable response to therapy.
Originally, radioimmunoassay has served as the basis for most determinations of CEA. Recently, sensitive and procedurally less complicated enzymeimmunoassays for carcinoembryonic antigen have been introduced.
However, the art lacks simple, rapid and reliable means for the immunoassay of antigens and analytes.
It is therefore an object of the present invention to provide improved means for assaying the content of antigen (compound, protein, or ligand) in a body fluid sample.
It is also an object of the invention to provide a new enzyme immunoassay (EIA) using multiple monoclonal antibodies having polyvalent reactivity in sandwich relation with a selected antigen or analyte.
It is another object of the invention to provide a new immunoradiometric assay (IRMA) using multiple monoclonal antibodies having polyvalent reactivity in sandwich relation with a selected antigen or analyte and yet having the advantage of polyclonal antibodies (See Nature, 296, 200-202, 1982).
A further object of the invention is to provide broadly applicable means for immunoassay of any of various exogenous or endogenous antigens, compounds, haptens or ligands.
These and other objects, features and advantages of the present invention will become apparent from the following description.